1. Field of the Invention
The present invention relates to an ink jet recording head, and more particularly to an ink jet recording head which discharges an ink droplet from an end of an ink discharge opening, such as an ink jet nozzle, by a pressure developed by an electro-mechanical transducer arranged along an ink flow path of the device.
2. Related Background Art
FIG. 1A shows a sectional view of the nozzle of the conventional recording head of the ink jet printer. The nozzle as shown in FIG. 1A is a Gould type nozzle. A nozzle body 31 is cylindrical with one end being conical and having a uniform diameter except for the conical portion. A discharge port 31a for discharging ink 35 from the nozzle body 31 as ink droplets is formed at the end of the nozzle body 31. The surface of the ink 35 exposed through the discharge port 31a forms a concave meniscus M.
A cylindrical piezoelectric element 32 which is an electro-mechanical transducing element for generating a discharging pressure for the ink droplets is fitted to an outer surface at the center of the nozzle body 31. It is integrated with the nozzle body 31 without clearance or gaps by adhesive material 33 such as epoxy resin.
A filter 34 is fitted and fixed near an open rear end of the nozzle body 31. The filter 34 blocks dirt and foreign materials in the ink 35 which flows to the left as shown by an arrow in the drawing from the rear end of the nozzle body 31 to the front end of the nozzle body, and also functions to match acoustic impedance at the front end and the rear end to a sound wave generated in the nozzle body 31 when the piezoelectric element 32 is driven.
In a recording mode, the piezoelectric element 32 receives the pulse voltage in accordance with the record data so that the piezoelectric element 32 contracts. As it contracts, a sound wave is generated and propagates in the ink 35 at a velocity of approximately 1200 m/s. FIG. 1B shows a manner of propagation. It shows a relationship between position in the nozzle body 31 and sound pressure at a time of application of the pulse voltage (t=0) and at a time shortly thereafter (t=t.sub.1), with the center of the graph corresponding to the center of the piezoelectric element 31. Because the ink 35 is discharged by the contraction pressure of the piezoelectric element 32 and the sound wave propagates as described above, the ink droplets are discharged from the discharge port 31a.
In the nozzle 30 described above, the sound wave generated by the drive of the piezoelectric element 32 and propagated to the rear end of the nozzle body 31 is reflected by the filter 34. The meniscus M is vibrated by the reflected sound wave. This vibration impedes efforts to shorten a period of ink drop discharge, that is, to improve a frequency characteristic and increase a recording speed.